Presentations 2016

Selective Groundwater Extraction for Agricultural Yield Optimization

Best Environmental Subsurface Science and Technologies (BESST)

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Subsurface quality grading of the groundwater supply throughout California began in earnest about a decade ago through miniaturization of down-hole flow and water chemistry measurement technologies as applied to municipal water supply wells. However, there has been a growing push in the agricultural sector for Selective Groundwater Extraction (SGE) – at least within California. SGE means that municipal groundwater producers and a growing number of agricultural concerns that use large quantities of groundwater now have the ability to pick and choose which subsurface layers of earth they extract groundwater from based in-well, down-hole, water quality grading. Many times, these new miniaturized technologies can be deployed in existing production wells without removing the pump from the well – such that an agricultural production well is catheterized in similar fashion to a patient receiving cardiac assist balloon pumping and angioplasty. In this sense the well is the patient. The line shaft turbine is the heart, the casing is the aorta, the well screen and surrounding formational stratigraphic units the complex of veins feeding groundwater to the well in different amounts and varying quality; where it is all mixed and blended in the casing before reaching the surface. In other cases, the farmer’s primary pump is removed and then reinstalled with small diameter access pipe (1” to 1.25” ID) to allow safe passage of the miniaturized tooling into the well and past the pump bowls and intake. In either case, the cost savings of using miniaturized technologies to diagnose flow and water quality contribution along the screens (perforations) of wells are significant in both the short and long term. Standard alternative approaches to dealing with water quality problems in agriculture are expensive and stem from not knowing how groundwater from the different stratigraphic horizons are blended inside the well before reaching the surface. The typical response for vineyards that experience difficulty with second plantings due to buildup of boron and sodium in the soil as well as walnut, almond and pistachio growers is to use expensive treatment and/or resort to building new wells. This presentation will explain the concept behind SGE including use of manipulated in-well hydraulics and engineered down-hole blending to achieve the desired water quality result through use of miniaturized diagnostic technologies. In one case, arsenic contribution will be examined which is of particular concern for ag facilities delivering potable drinking water to their employees. In another case, subsurface boron distribution will be explained.